It's Flu Season: Here's What Happens When You Take Too Many Vitamins

During cold and flu season, it’s normal to be a little nutty about staying healthy. Whether it’s obsessively washing your hands or giving yourself a vitamin C boost by dropping a tablet into your water, many of us take every possible precaution to avoid getting sick.

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Why vitamin C? It’s a powerful antioxidant linked to a healthy immune system. It's also the primary ingredient in dietary supplements such as Airborne and Emergen-C that you’ll typically find in the same aisle as cold and flu medicine.

By delivering a megadose of vitamin C and other key nutrients such as vitamin A, vitamin E, Zinc, and Selenium, these supplements claim to boost your immune system. Just one dose of Emergen-C or Airborne packs 1000mg of vitamin C, which is over 1000% of your recommended daily intake. That’s over ten times the recommended amount, given that adults need only 75mg to 90mg of vitamin C per day.

Is a megadose of vitamin C really necessary? And, better yet, can it cure a cold?

The truth is, dietary supplements are not meant to treat, cure, or prevent illness. In most cases, they should only be used for a short-term period and shouldn't replace nutrients you can get from food. If taken in high doses for longer periods of time, supplements may lead to adverse health effects and even vitamin toxicity. And because some supplements may be harmful when combined with other drugs, it’s always best to talk to your doctor before taking them.

So, what does taking too many vitamins look like? What are the potential health risks? The Institute of Medicine determines Tolerable Upper Level Intakes (ULs), or the maximum amounts, of vitamins you can safely take per day. When we matched key vitamins found in Airborne and Emergen-C with their associated ULs, it was much easier to see just how big of a dose these supplements provide.

Upper Limits for Adults

Airborne (1 tablet)

Emergen-C (1 packet)

Vitamin C

2000 mg

1000 mg (1167% DV)

1000 mg (1167% DV)

Vitamin A

10,000 mg

2000 mg (40% DV)

n/a

Vitamin B6

100 mg

n/a

10 mg (500% DV)

Zinc

4 mg

8 mg (53% DV)

2 mg (13% DV)

Selenium

400 mcg

15 mcg (21% DV)

n/a

Source: Institute of Medicine / Amazon

Airborne recommends taking no more than three tablets per day, but this is still over 3000% more vitamin C than you actually need. Emergen-C also cautions against using more than two packets. To find what can happen if you surpass daily limits, we referenced each vitamin in the National Institutes of Health’s Office of Dietary Supplements.

Vitamin C

The NIH reports that most people who consume too much vitamin C from supplements experience gastrointestinal issues such as diarrhea, nausea, and stomach pain. While the recommended daily amount of vitamin C supports your body’s immune system health, an excess amount will most likely be flushed out through your urine.

VItamin A

One Airborne tablet packs nearly half a day’s worth Vitamin A (Emergen-C does not contain this nutrient). Specifically, Airborne contains retinyl acetate, a type of preformed Vitamin A often used in dietary supplements. In food, preformed vitamin A is found in meat, poultry, and dairy products. NIH links excessive amounts of preformed Vitamin A to dizziness, nausea, and headache.

Vitamin B6

According to the NIH, excessive vitamin B6 intake from supplements for a year or more can temporarily cause nerve damage, increased sensitivity to sunlight, irritated skin, nausea, and heartburn. One Emergen-C packet delivers more than enough vitamin B6—over seven times the recommended amount of 1.3 mg per day for adults.

Zinc

In healthy doses, Zinc is associated with a strong immune system. Consuming too much zinc on a regular basis, however, can cause nausea, vomiting, appetite loss, stomach pain, headache, and diarrhea. One Airborne tablet packs over half of your daily recommended amount of zinc (between 8 and 11mg for adults)

Selenium

Like vitamin C, selenium boasts immune-boosting benefits when consumed in recommended amounts (55 mcg per day for adults). Excessive intake of selenium can lead to adverse effects such as brittle nails and teeth, a metallic taste in your mouth, nausea, diarrhea, irritability, nervous system problems, and more.

Photo: Hector Manuel Sanchez

The Bottom Line: Staving off your cold or preventing the flu with a supercharged dose of vitamins is simply not a reliable remedy.

And while you can certainly use Airborne tablets to jazz up your water every once in a while, don’t make it a daily habit. One large dose of vitamins isn’t going to hurt you, but taking excessive amounts over a longer period of time could.

If you’re looking to boost immunity, we suggest doing it the natural way—through your diet. From whole grains to salmon to kale, there’s an abundance of anti-inflammatory, immunity-boosting foods out there worth piling onto your plate. Compile your favorite healthy cold- and flu-busting recipes so you can easily whip up a nutrient-rich meal when you’re feeling under the weather. (Need inspiration? Our Immunity Soup is the perfect place to start.)

And if you’re trying to avoid getting sick, you can never go wrong with tried-and-true methods such as washing your hands, getting enough sleep, and drinking plenty of water.